1. Field of the Invention
This invention relates in general to a data communication system and particularly to a relay system in facsimile communication.
2. Description of the Prior Art
As one form of facsimile communication, proxy communication is often used. In proxy communication, image information from a facsimile source station is once transmitted to a facsimile relay station where the image information is temporarily stored in its image memory and then the image information is transmitted from the relay station to a facsimile destination station designated by the source station. Typically in this mode of operation, upon transmission of image information from the relay station to the destination station, the relay station sends a relay complete report to the source station. Thus, until the source station receives the relay complete report from the relay station after having transmitted address of destination and image information with or without designated relaying time to the relay station, it cannot be sure at the source station as to whether the image information might have been transmitted to a wrong station due to an error in address information caused for example by a transmission line error. In addition, even if there has been no error in transmission procedure, there could be caused a loss or disturbance of image information, which cannot be detected at the source station.
Under the circumstances, in accordance with the prior art relay system, communication is interrupted if a line error has occurred five times or more in succession or the number of line errors per page has exceeded a predetermined number while the relay station is receiving image information, or alternatively, the image information of preceding page, which has been received previously, is transmitted to the destination station. However, in accordance with these prior art schemes, it cannot be checked at the source station as to whether the line error occurred is at a critical or non-critical portion of information, and, furthermore, transmission of information to a wrong station as described above cannot be prevented.